The invention is directed to a gold free alloy for the firing on of ceramic compositions, especially for industrial dental purposes.
For many years gold containing noble metal alloys having high contents of gold have been used for artificial teeth overcoated with dental procelain. These known alloys are very well suited for this purpose and lead to good adhering, normally crack free procelain overlays. Because of their relatively low melting temperatures they are readily workable and because of their high portion of noble metal they are very resistant to corrosion.
Because of the high price of gold and the high density of these known alloys there have been previously many attempts to replace these high gold containing alloys through those based on silver-palladium or on a non-noble metal basis. Such non-noble metal alloys previously always contained nickel as the chief component, besides, in many cases, beryllium also as a component of the alloy. Both elements however, are toxic and therefore little suited for use in the human mouth.
Besides these nickel alloys generally show a high solidus temperature which makes their use in dental laboratories very difficult. Besides, compared to high gold content alloys, they have a reduced resistance to corrosion which, to be sure can be improved by a high chromium content. However, the addition of chromium leads to green coloration of the porcelain in the firing on of porcelain, which coloration is undesired.
The same disadvantage is also shown by the known fired on alloys based on silver-palladium.
Recently, there have become known non-noble metal alloys based on cobalt for the firing on of dental porcelains which contain either no noble metals or insignificant amounts thereof. Since cobalt, however, in contrast to nickel is only resistant to corrosion with chromium contents of more than 25 weight %, this makes the green coloration of the porcelain in the firing noticeable. Besides in these alloys the adhesive strength of the fired porcelain is not sufficient.
Therefore it was the problem of the present invention to find gold free alloys for the firing on of ceramic compositions, especially for industrial dental purposes which contain no toxic components, are corrosion resistant, have a relatively low melting point, do not cause coloration of the ceramic compositions in the firing and guarantee an adhesive bond.